Centrifugal pumps are known, for instance from European patent applications EP1903216 and EP1906029. Such pumps can be used for dredging purposes, i.e. to pump slurry comprising water and dredged materials. An example of such a centrifugal pump is depicted in FIGS. 1 and 2.
FIGS. 1 and 2 schematically depict an example of such a known centrifugal pump 1, both Figures showing a cross-sectional view in different directions. The pump 1 comprises a pump housing 2 shaped like a volute (spiral casing). The pump housing 2 comprises a circumferential wall 3, a pump casing 20 and a shaft cover 40. The circumferential wall 3 comprises a spout-shaped outlet 5 attached tangentially to the circumferential wall 3. The junction between the inner surface of the tangential outlet 5 and the inner surface of the circumferential wall 3 of the pump housing 2 defines what is known as a cutwater 4. The pump housing 2 also has an axial inlet 6, shown in FIG. 2.
The circumferential wall 3 may have a U-shaped or semicircular cross-section, comprising two (parallel) legs 31 extending in a radial inward direction and a middle part connecting the two legs forming the outer wall 32 of the circumferential wall. This outer wall 32 may be a straight part or may be curved.
The outer wall 32 spirals outwardly about the axial rotation axis A of the pump 1 (defined below) towards the tangential outlet 5.
A rotor 7 is attached in the pump housing 2 such that it may rotate about an axial rotation axis A. The rotor 7 comprises rotor blades 15, a shaft shield 11 and a suction shield 12. The rotor 7 also comprises a central boss 9 which may be fastened to a drive shaft (51). The shaft shield 11 extends from the central boss 9. The shaft shield 11 forms a first wall for delimiting the flow within the rotor 7. Axially set apart from the shaft shield 11, the rotor 7 has the suction shield 12 which defines a second wall for delimiting the flow within the rotor 7. The suction shield 12 has an axial supply 14 which is aligned with the axial inlet of the pump housing 2.
A plurality of rotor blades 15 are fastened between the shields 11, 12. In this illustrative embodiment, the rotor 7 comprises three rotor blades 15. The rotor blades 15 each extend substantially radial to the rotation axis A. Between the radial outer ends 17 of the rotor 7 and the inner surface of the circumferential wall 3 of the pump housing 2 there is a circumferential channel 19.
The circumferential wall 3 of the pump housing 2 substantially closes the inner space of the rotor 7 along its outer circumference between the shields 11, 12 and may have a rounded shape.
In order to provide a strong pump, the pump housing 2 further comprises a pump casing 20 and a shaft cover 40, both attached to the circumferential wall 3.
The pump casing 20 is attached to the pump housing 2, i.e. to the circumferential wall 3, by suitable connection means 22. The pump casing 20 has a central opening which may form the axial supply 14 or may surround the axial supply 14. The pump casing 20 may comprise a stepped part 23 and reinforcing ribs 21 (not shown in FIGS. 1 and 2). The term pump casing in this text is used to refer to a part of the pump housing 2 extending between the central opening to the circumferential wall 3. The pump casing 20 may also be referred to as the suction cover or suction lid 20.
The shaft cover 40 (or shaft lid 40) is also attached to the circumferential wall 3 opposite the pump casing 20, by suitable connection means 42. The shaft cover 40 also has a central opening to allow a drive axis 51 of a pump motor 50 to be connected to the rotor 7.
During operation, the drive axis 51 and the rotor 7 rotate about the rotation axis A. Between the rotor blades 15, the mass to be pumped is forced radially outward into the pump housing 2 under the influence of centrifugal forces. Said mass is then entrained in the circumferential direction of the pump housing 2 toward the tangential outlet spout 5 of the pump housing 2. The pumped mass which, after leaving the rotor 7, is entrained in the circumferential direction of the pump housing 2 flows largely out of the tangential outlet of the pump housing 2. A small amount of the entrained mass re-circulates, i.e. flows along the cutwater 4 back into the pump housing 2.
When such pumps are used for dredging, the pumps may be subjected to extreme wear, especially the rotor 7 and the circumferential wall 3. Therefore preferably wear resistant material is used. However, these materials are in general not well suited for construction purposes, as they are usually brittle. An example of such a material is white cast iron such as maxidur.
As a result of the pumping, high pressure will be generated forcing the pump casing 20 outwardly. High loads may be transferred via connection means 22. From FIG. 2 it can be seen that these loads may introduce a bending moment in the circumferential wall 3 of the pump housing 2, as the leg 31 to which the pump casing 20 is attached is forced in an outward direction. To prevent introducing a bending moment, or keeping the bending moment relatively small, in the circumferential wall 3 of the pump housing 2, it is known to position the connection means 22 more outwardly than shown in FIG. 2, i.e. along the outer circumference of the circumferential wall 3 of the pump housing 2, at the position where the circumferential wall 3 is relatively thick (seen in the direction of the connection means 22) and is thus able to take up high loads. An example of this is the LSA-S Series Slurry Pumps of GIW Industries.
This will result in lower stresses in the circumferential wall 3 of the pump housing 2 and reduces the chance of deformation of the circumferential wall 3.
Further examples of connection means provided along the outer circumference are provided by DE2541422A1, GB719285A and FR567370A.
WO2009149511 shows a pump assembly with a pump housing comprising two casting parts which are joined together about the periphery of the two side casing parts, without the use of a circumferential wall as described above. The two side casing parts comprise apertures to allow the two side casing parts to be joined together by bolts. One of the side casing parts also comprises apertures for receiving liner locating and fixing pins for locating the main liner or volute and the pump outer casing relative to another.